1. Field of the Invention
The present invention relates to an actuator driving method and an actuator driving apparatus for driving an actuator for moving a head and, more particularly, to an actuator driving method and an actuator driving appatatus for PWM-driving the actuator in a storage disk device for reading or reading/writing information from a storage disk by the head.
2. Description of the Related Art
A storage disk device such as a magnetic disk device etc has been widely utilized as a storage device of a computer etc. A high-density record and a decrease in the electric power consumed are demanded of this type of storage disk device. For reducing the electric power consumed by this magnetic disk device, a PWM driving system is applied to a driving stage of the actuator (VCM).
FIG. 5 is a diagram showing a construction of the prior art. FIG. 6 is an explanatory diagram of the prior art.
As illustrated in FIG. 5, the magnetic disk device includes a magnetic disk 101 and a magnetic head 90. A servo signal is recorded per sector on the magnetic disk 101. The magnetic head 90 reads and writes the information from and to the magnetic disk 101. The head IC 91 amplifies the signal read by the magnetic head 90.
A read channel IC 92 selects a read signal transmitted from the head IC. A servo signal demodulator 93 demodulates a servo signal from the read channel IC 92 into a position signal. A servo gate generation circuit 94 generates, synchronizing with rotations of the magnetic disk 101, a servo gate signal indicating that the magnetic head 90 is located in a servo region recorded with the servo signal of the magnetic disk 101.
A control circuit 95 detects a present position of the head in accordance with the position signal, and generates a current indication value corresponding to a distance from a position to be sought. A digital/analog converter 96 converts the current indication value given from the control circuit 95 into an analog quantity. A PWM (Pulse Width Modulation) driver 97 generates a drive current having a pulse width corresponding to the current indication value.
A linear driver 98 generates a drive current of which a magnitude corresponds to the current indication value. A coil driving circuit 99 has four power transistors Q1-Q4. A coil VCM of the actuator is connected to the four power transistors Q1-Q4. A current detection resistor RS detects an electric current flowing to the coil VCM.
A differential amplifier 100 generates an inter-terminal voltage of the current detection resistor RS, and feeds back this voltage to the PWM driver 97 and the linear driver 98. An inverting circuit 102 inverts a PWM enable signal and outputs the inverted signal to the linear driver 98.
In the construction described above, the control circuit 95 detects the present position from the servo information during seek control (coarse control), and generates the current indication value corresponding to a distance at which a seek movement is made. Further, the control circuit 95 obtains a deviation from the center of the tracks from the servo information and generates the current indication value for the duration of an on-track (fine control) operation.
Then, as shown in FIG. 6, during the coarse control, the PWM enable signal is set high, and the PWM driver 97 is operated. The PWM driver 97 thereby generates the drive current having the pulse width corresponding to the current indication value. Therefore, the coil VCM of the actuator is PWM-driven.
Thus, the PWM drive makes the driving pulse width change, and hence the electric power consumed can be largely reduced.
On the other hand, if the PWM drive is executed during the on-track operation, the switching noises due to the VCM drive current are superposed on a regenerated signal of the head 90. For preventing this noise superposition, during the on-track control under which the read/write processes are executed, the PWM enable signal is set low, while the operation of the PWM driver 97 is inhibited. With this inhibition, the linear driver 98 is operated by an inverted signal of the PWM enable signal.
The linear driver 98 thereby generates the drive current of which a magnitude corresponds to the current indication value. Therefore, the coil VCM of the actuator is linearly driven. During this on-track operation, the current indication value defined as a control quantity is small, and hence, even when linearly driven, the electric power consumed is small.
Thus, according to the prior art, the PWM drive with the small amount of electric power consumed is carried out during the seek operation, thereby restraining the consumption of the electric power of the disk device.
There arise, however, the following problems inherent in the prior art.
It is required that the servo information be read during also the seek control. If switching of the drive current of the actuator VCM is effected during the read operation of the servo information, the servo signal is overlapped with the switching noises thereof. Hence, this leads to such a problem that the precise servo signal can not be obtained.
In particular, when enhancing the recording density, the servo signal might become weak against the noises, and the precise servo signal is hard to obtain.
It is a primary object of the present invention to provide an actuator driving method and an actuator driving apparatus in a storage disk device, which are capable of preventing a servo signal from being overlapped with switching noises.
It is another object of the present invention to provide an actuator driving method and an actuator driving apparatus in a storage disk device, which are capable of obtaining a precise servo signal even when executing a PWM drive during seek control.
It is still another object of the present invention to provide an actuator driving method and an actuator driving device in a storage disk device, which are capable of maintaining a seek velocity even when halting the PWM drive during the seek control.
According to one aspect of the present invention, a storage disk apparatus comprises a storage disk, a head for reading information from the storage disk, a PWM driver for generating a drive current having a pulse width corresponding to a current indication value, a linear driver for generating a drive current of which a magnitude corresponds to the current indication value, an actuator, driven by the drive current, for moving the head, and a control circuit for generating the current indication value for positioning the head from the servo information read from the storage disk by the head.
An actuator driving method thereof comprises a step of PWM-driving the actuator by the PWM driver, and a step of effecting a switchover from the PWM drive to a linear drive by the linear driver during a period for which the control circuit reads the servo information during the PWM drive.
According to the present invention, first, the PWM drive is halted during the period for which the control circuit reads the servo information. It is therefore feasible to prevent the servo information from being overlapped with switching noises due to the PWM drive.
Second, during the halt period of the PWM drive, the linear drive is conducted. Hence, the seek velocity can be prevented from decreasing even when stopping the PWM drive.
According to another aspect of the present invention, the PWM drive step comprises a step of applying the current indication value and selecting the PWM drive. According to still another aspect of the present invention, the actuator driving method further comprises a step of detecting from the servo information that the head arrives at the vicinity of a target position, and executing the switchover from the PWM drive to the linear drive.
According to still another aspect of the present invention, the switchover step comprises a step of selecting the linear drive in accordance with a servo gate signal indicating that the head is located in a servo information write region on the storage disk.
According to a further aspect of the present invention, the switchover step comprises a step of selecting an output of the linear driver in accordance with AND of the servo gate signal and a PWM enable signal for operating the PWM driver.
Other features and advantages of the present invention will become readily apparent from the following description taken in conjunction with the accompanying drawings.